Is it permissible for the tenant to deduct the costs of apartment improvements from the rent without the landlord's permission?

The landlord is not obligated to pay the tenant for improvements and additions made by the tenant to the apartment without the landlord's permission, because the tenant, in doing so, is a volunteer (one who donates/undertakes an act gratuitously). Furthermore, the repair of the rented property is the responsibility of the owner, not the tenant. Therefore, the tenant must pay the full rent, and it is not permissible for him to deduct what he spent. However, we advise the landlord to assist the tenant in bearing some of these costs.